Muscle Tissue: Skeletal, Cardiac, Smooth - Anatomy and Physiology
- Why do the cells of single-unit (visceral) smooth muscle contract together as a unit?
- Gap junctions electrically couple neighboring cells, so excitation spreads from cell to cell.
- What is the shape and nucleus arrangement of a smooth muscle cell?
- Spindle-shaped (tapered at both ends) with a single central nucleus.
- Which structures join cardiac muscle cells end to end?
- Intercalated discs, which contain gap junctions for electrical coupling and desmosomes for mechanical strength.
- Why can cardiac muscle not be tetanized?
- Its long refractory period lasts nearly as long as the contraction, so the cell relaxes before it can be restimulated.
- Which two muscle tissues are under involuntary control?
- Cardiac and smooth muscle. Skeletal muscle is the only voluntary type.
- Which calcium-binding protein in smooth muscle takes the role that troponin has in skeletal muscle?
- Calmodulin. Calcium-calmodulin activates myosin light chain kinase to start contraction.
- Which muscle tissue has striated, long cylindrical cells with many nuclei at the periphery?
- Skeletal muscle. Each fiber forms by the fusion of many embryonic cells.
- In smooth muscle, what structures anchor thin filaments in place of Z discs?
- Dense bodies.
- Which muscle tissue has branched striated cells, usually with one or two central nuclei?
- Cardiac muscle.
- Which cells allow limited regeneration of skeletal muscle after injury?
- Satellite cells, stem cells lying between the fiber and its endomysium.
- Which of the three muscle tissues has the greatest capacity to regenerate?
- Smooth muscle. Skeletal muscle regenerates only partly, and cardiac muscle very little.
- Which muscle tissue lacks striations?
- Smooth muscle. Its actin and myosin are not arranged in sarcomeres.